This feature was removed in March 23
When a page is created an 'extras' file is also created. It can be accessed and edited in Admin/pages 'Get extras'. The extras file is displayed by adding a dollar sign $ to the first line of the page text. It can be hidden by removing the dollar sign.
The extras file text is not auto-formatted into paragraphs like the main page content. For separate paragraphs, HTML paragraph tags should be used.
The file's content appears below the main content.